Apparatus and Method for Cleaning a Well

ABSTRACT

The present invention relates to apparatus and a method for cleaning a well. In an embodiment, the apparatus ( 10 ) includes a well cleaning tool ( 12 ) coupled to a support string  26 , which may be located in well tubing ( 14 ) to permit cleaning of the well tubing ( 14 ). The cleaning tool ( 10 ) may restrict fluid flow past the tool, for example, in an annular space between the tool ( 12 ) and the well tubing ( 14 ). Further, the tool ( 12 ) can be translated relative to the well tubing ( 14 ) to displace fluid along the well tubing ( 14 ) and thus clean the well.

The present invention relates to well cleaning in the field of the oil and gas exploration and production industry. In particular, but not exclusively, the present invention relates to apparatus and a method for cleaning a well.

In the oil and gas exploration and production industry, a borehole is drilled from surface to gain access to well fluids in subterranean rock formations. The borehole is typically drilled to a first depth, and well tubing known as casing is then located in the drilled section and cemented in place, both to support the drilled rock formations and to prevent formation fluids from entering the borehole. The borehole is then extended to a further depth, and a smaller diameter well tubing known as a liner is run-in to the extended section, coupled to the lower end of the casing, and also cemented in place. Once the borehole has been extended and lined to a desired depth, a completion string is run-in to enable completion of the well and recovery of well fluids from a particular rock formation.

However, during drilling of the borehole, a drilling fluid known in the industry as ‘drilling mud’ is utilised to carry drill cuttings to surface; to form a skin on drilled rock formations to prevent mud loss; to cool the drill bit; to drive a downhole motor coupled to the drill bit (if used); and to maintain hydrostatic pressure overbalance across the rock formations, to prevent blowout of formation fluids.

Accordingly, before the well can be completed, it is necessary to clean the borehole by removing residual drilling mud, formation fluids, drill cuttings and the like from the well tubing. This has conventionally been achieved by pumping relatively large volumes or ‘pills’ of a viscous fluid downhole. The viscous fluid is often of greater weight (density) than the drilling mud, and serves to carry the drilling mud, cuttings and the like to surface. These pills of viscous fluid are followed by a completion fluid, typically a saturated salt solution known as ‘brine’, which is used to replace the fluids removed from the borehole. The weight of the brine is chosen to suit the particular well, to ensure that the well remains overbalanced both during and subsequent to the cleaning operation.

This cleaning operation presents a number of problems, particularly on offshore rigs where deck space is at a premium. In particular, a great deal of deck space is required to store the concentrates of chemicals needed to make the pills of viscous fluid needed to clean the well. Furthermore, a number of valuable mixing pits are needed to store the prepared completion brine and to prepare the pills of viscous fluid, and these tanks need to be cleaned before the brine or viscous fluid can be pumped into the tanks, as they may previously have been used for storing drilling mud.

Also, when the viscous pills and completion brine are pumped downhole, a large fluid interface is formed between the drilling mud and the viscous fluid/brine. This interface fluid is a mixture of fluids including drilling mud, brine and the viscous fluid and cannot be cleaned to recover the valuable drilling mud. The interface fluid must therefore be temporarily stored on the rig either for subsequent shipping offsite, or for injection into an abandoned well. As the volume of interface fluid is relatively large, this utilises a significant number of mixing pits.

Additionally, as the drilling mud is designed to coat the surfaces of the drilled formations, it has been found difficult to remove the mud from the walls of the well tubing. To overcome this, it is necessary to pump the pills of viscous fluid and the brine at relatively high fluid flow rates, whilst rotating the drill string in the well tubing. This promotes turbulent flow, which assists in removing mud solids adhered to the wall of the casing; carrying the removed solids to surface; and in reducing the size of the fluid interface.

However, maintaining a high fluid flow rate has a consequent effect upon costs. Also, if it is desired to re-inject the interface fluids into an abandoned well, it is necessary to reduce the fluid flow rate to suit the injection rate that may be achieved using a cuttings re-injection unit, with a consequent effect upon the injected fluid flow rate and thus on the volume of interface fluids. Also, it is often necessary to continue pumping the viscous fluid/brine for long periods of time, often twenty-four hours or more, in order to achieve a desired level of cleaning. This results in significant delays in completing the well, with associated cost implications.

Even when this cleaning operation has been carried out, it has been found that the well is often not sufficiently clean, which can create problems both when the well is completed, and during subsequent recovery of well fluids. For example, it has been found that the cleaning operation often does not remove relatively large or heavy solids from the cased borehole. In an effort to address this problem, tools have been developed for scraping the casing and for filtering solids from the fluid in the cased borehole. However, it has been found that solids often still remain in the completion fluid, as the cleaning tool simply filters the fluid in the borehole.

It is amongst the objects of embodiments of the present invention to obviate or mitigate at least one of the foregoing disadvantages.

According to a first aspect of the present invention, there is provided a well cleaning tool for location in well tubing to be cleaned on an associated support string, the cleaning tool adapted to be configured to restrict fluid flow past the tool and to be translated relative to the well tubing to displace fluid along the well tubing and thereby clean the well.

The invention therefore provides a cleaning tool which may be utilised to remove or displace fluids and any entrained solids from the well tubing by translation of the cleaning tool along the tubing. Thus, for example, drilling mud, well fluids and any drill cuttings or other solids present in the well tubing following drilling and installation of the well tubing may be removed using the cleaning tool, in preparation for completion of the well.

It will be understood that the cleaning tool cleans the well tubing by urging fluid/solids along the tubing ahead of the cleaning tool in the direction of travel of the tool.

Preferably, the tool is adapted to be configured such that fluid flow past the tool is substantially or completely prevented. The tool may be adapted to be configured to restrict fluid flow past the tool along an annulus defined between the well tubing and the support string.

The cleaning tool may be movable between a first configuration where fluid flow past the cleaning tool is permitted, and a second configuration where fluid flow past the cleaning tool is restricted. Preferably, in the second configuration of the tool, fluid flow past the tool is substantially or completely prevented. The first configuration may be a deactivated, running configuration and the second configuration may be an activated, cleaning configuration. The cleaning tool may be adapted to be run into the well tubing in the deactivated configuration and subsequently moved to the activated configuration for cleaning the well tubing. This may facilitate positioning of the cleaning tool at a desired location within the well tubing, and subsequent activation of the cleaning tool for carrying out a cleaning operation. Alternatively, the cleaning tool may be adapted to be run into the well tubing in the activated configuration and subsequently moved to the deactivated configuration. This may facilitate cleaning of the well tubing when the tool is run-in, and subsequent movement of the tool to the deactivated configuration for recovery of the tool.

In a further alternative, the cleaning tool may be adapted to permit fluid flow in one direction past the tool, and to restrict fluid flow past the tool in an opposite direction. The cleaning tool may be adapted to be configured such that when the tool is translated in a first direction along a length of the well tubing, fluid flow past the cleaning tool is permitted; and when the tool is translated in a second, opposite direction along the length of the tubing, fluid flow past the cleaning tool is restricted. The cleaning tool may therefore be arranged such that the tool automatically restricts fluid flow when the tool is translated in a first direction along the well tubing, but permits fluid flow when the tool is translated in a second, opposite direction. For example, in embodiments of the invention, fluid flow past the tool may be permitted during run-in of the tool into the well tubing, and may be restricted when the tool is pulled-out of the well tubing. The first direction may therefore be a run-in direction and the second direction a pull-out or run-out direction. In alternative embodiments, fluid flow past the tool may be restricted during run-in of the tool into the well tubing, and permitted when the tool is pulled-out of the well tubing. The first direction may therefore be a run-out direction and the second direction a run-in direction.

Preferably, the cleaning tool is adapted to abut or engage a wall of the well tubing in order to restrict fluid flow. Accordingly, when the cleaning tool is brought into abutment with the tubing wall, translation of the tool along the well tubing urges fluid along the tubing. The cleaning tool may be adapted to sealingly abut or engage the wall of the well tubing to substantially or completely restrict fluid flow past the cleaning tool. In embodiments of the invention, the cleaning tool may be movably mounted relative to a support string, and may also be adapted to abut or engage a surface of the support string, and optionally to sealingly abut or engage the surface of the support string. Alternatively, the cleaning tool may be coupled to tubing of the support string, for example through a threaded connection, and therefore it may not be necessary to arrange the cleaning tool to sealingly abut or engage the surface of the support string.

Most preferably, the cleaning tool comprises at least one abutting element for abutting or engaging the wall of the well tubing, the element serving for permitting and restricting fluid flow past the tool. The abutting element may be radially movable or otherwise outwardly movable relative to a body of the tool. The abutting element may be adapted to extend from or to be upstanding from a body of the tool. The abutting element may be movable between a deactivated configuration and an activated configuration, which may correspond to deactivated and activated configurations of the tool, for selectively engaging an internal surface of the tubing. For example, it may only be desired to arrange the abutting element to abut an internal surface of the tubing during passage of the tool in a selected direction along a length of the tubing. The abutting element may be movable between a collapsed and extended or deployed positions corresponding to the deactivated and activated configurations, for abutting the well tubing. The abutting element may be adapted to be biased into abutment with the well tubing wall. In a variation, the abutting element may be adapted to be moved between a deactivated configuration where the abutting element abuts the well tubing wall but permits fluid flow, and an activated configuration where the abutting element is arranged to restrict fluid flow. For example, the abutment element may be urged into enhanced abutment with the tubing wall to restrict fluid flow. In preferred embodiments, the tool comprises a plurality of abutting elements which may be fins, ridges or the like extending from a surface of a body of the tool.

Alternatively, the abutting element may be resilient and may be adapted to be deflected to permit fluid flow past the tool in one direction and to restrict fluid flow past the tool in an opposite direction. To facilitate this, the abutting element may comprise a resilient annular ring or the like extending from a body of the tool.

The tool may comprise an actuating mechanism for moving the tool, in particular the abutting element, between the deactivated and activated configurations. In particular preferred embodiments, the actuating mechanism may be adapted to exert a radial actuating force on the abutting element through an axial force applied to or generated by the mechanism. Where the tool comprises a plurality of fins or the like, the fins may be compressed and thus urged radially outward to abut the tubing wall.

The cleaning tool may be adapted to be hydraulically actuated for configuring the tool to restrict fluid flow, and may comprise a hydraulic actuating mechanism for moving the tool between the first and second configurations. For example, the tool may comprise at least one piston for configuring the tool to restrict fluid flow. The actuating mechanism may be adapted to urge the abutting element between the deactivated and activated positions. The piston may be actuated in response to an applied control signal or applied fluid pressure, for example via control line or by differential fluid pressure between an interior and an exterior of the tool. The actuating mechanism may comprise a burst disc or the like for isolating the piston from applied fluid pressure until such time as fluid at a determined pressure is applied to rupture the disc. Thus the tool may be run-in to a desired location within the tubing with the abutting element held in a deactivated or activated position until fluid pressure at a determined level is applied to rupture the burst disc and move the abutting element from the deactivated configuration to the activated configuration, or vice-versa. It will be understood that this determined level may be significantly higher than the fluid pressure normally experienced by the tool, and this may prevent premature actuation of the abutting element.

Alternatively, the cleaning tool may be mechanically or electro-mechanically actuated for configuring the tool to restrict fluid flow, and may comprise a mechanical or electro-mechanical actuating mechanism for moving the tool between the first and second configurations. For example, the tool may comprise a biasing mechanism for urging the tool between the deactivated and activated configurations, and a shear pin, locking ring or the like for retaining the tool in one of said configurations. The shear pin may be arranged to maintain the tool in the deactivated configuration, permitting fluid flow past the tool until such time as the pin is sheared, whereupon the tool may move to the activated configuration, restricting fluid flow, or vice-versa. This may prevent premature actuation of the abutting element. The shear pin may be sheared by applying a jarring force to the support string, or by a release mechanism arranged to exert a force on the shear pin to release the pin. Where the cleaning tool comprises an electro-mechanical actuator, the tool may be actuated in response to an applied control signal.

It will be understood that in further alternative embodiments, the tool may comprise a combination of hydraulic, mechanical and/or electro-mechanical actuators.

The tool, in particular the abutting element may define a cleaning surface for cleaning or wiping an internal wall of the well tubing. Alternatively, the tool may comprise at least one cleaning element separate from the abutting element, the cleaning element defining the cleaning surface. The cleaning surface may be adapted to scrape, wipe or abrade the internal wall of the well tubing during translation of the cleaning tool through the tubing, to remove solids such as mud residues, scale or the like adhered to the wall of the well tubing. The cleaning surface may take the form of a blade, fin, scraper, abrader, brush or the like, or the tool may comprise a combination thereof.

The cleaning tool may be adapted to be movably mounted relative to the support string, and may comprise a body mounted for movement relative to the support string along a length thereof. This may facilitate movement of the tool along the string, and/or movement of the string within and thus relative to the tool. Accordingly, the cleaning tool may be adapted to be run-in to the well tubing along a support string already located within the tubing, without requiring the string to be pulled out. For example, the cleaning tool may be run-in on a drill string located in the well tubing. The cleaning tool may therefore comprise a generally annular member in the form of a swab, plug or the like, adapted to be pumped down the well tubing along the support string.

Alternatively, the cleaning tool may be adapted to be secured against movement relative to the support string and may be coupled to sections of the support string by threaded connections or the like. This may facilitate translation of the tool relative to the well tubing by translation of the support string along a length of the tubing. It will be understood however that where the tool is movably mounted relative to the support string, the tool may also be adapted to be secured relative to the support string, to facilitate translation of the tool along the well tubing using the support string, if desired.

According to a second aspect of the present invention, there is provided apparatus for cleaning a well, the apparatus comprising:

a support string adapted to be located in well tubing to be cleaned; at least one well cleaning tool coupled to the support string, the well cleaning tool adapted to be configured to restrict fluid flow past the tool and to be translated relative to the well tubing to displace fluid along the well tubing and thereby clean the well.

The cleaning tool may be adapted to be translated along the support string relative to the well tubing from a downhole location and in a direction towards the surface, to displace fluid in the well tubing along the tubing to surface. To achieve this, replacement fluid such as completion fluid may be pumped into the well tubing down the support string, to create a pressure differential across the tool and urge the cleaning tool along the support string.

Alternatively, the cleaning tool may be adapted to be translated along the support string relative to the well tubing in a direction from surface to a downhole location, to displace fluid in the well tubing and up the support string to surface. To achieve this, replacement fluid such as completion fluid may be pumped into the well tubing down an annulus between the tubing and the string, to create a pressure differential across the tool and urge the cleaning tool along the string.

In a further alternative, the cleaning tool may be adapted to be secured relative to the support string and to be translated relative to the well tubing in a direction towards the surface, to displace fluid in the well tubing along the tubing to surface, by translating the support string along the well tubing. Replacement fluid such as completion fluid may be adapted to be pumped into the well tubing along the support string. In a variation, the cleaning tool may be adapted to displace fluid along the well tubing during run-in of the support string, displaced fluid passed to surface through the support string and completion fluid pumped into the well tubing behind the cleaning tool.

Preferably, the apparatus comprises a plurality of cleaning tools, and may comprise a first cleaning tool adapted to define a first, cleaning diameter for cleaning a first section of well tubing of a corresponding first diameter and a second cleaning tool adapted to define a second, cleaning diameter for cleaning a second section of well tubing of a corresponding second diameter. This may facilitate cleaning of a length of well tubing having varying internal diameter along a length thereof, such as is typically found downhole, for example, in a transition from larger diameter casing to smaller diameter liner.

At least one of the cleaning tools may be adapted to be movably mounted relative to the support string, and may comprise a body mounted for movement relative to the support string along a length thereof. This may facilitate movement of the tool along the string, and/or movement of the string within the tool. At least one other one of the cleaning tools may be adapted to be secured against movement relative to the support string and may be coupled to sections of the support string by threaded connections or the like. This may facilitate translation of the tool relative to the well tubing by translation of the support string along a length of the tubing. Accordingly, at least one of the cleaning tools may be movable relative to at least one other cleaning tool.

Preferably, a lower cleaning tool is secured against movement relative to the support string, and an upper cleaning tool is movably mounted relative to the support string. This may facilitate translation of the support string within and relative to the upper cleaning tool, the support string carrying the lower cleaning tool to bring the lower cleaning tool to a position adjacent or close to the upper tool. This may enable the lower tool to be used to clean a lower section of well tubing, and to carry fluid out of said lower section and past the upper cleaning tool, whereupon the upper cleaning tool may be translated relative to an upper section of well tubing, to carry the fluid displaced from the lower section, as well as fluids in the upper section, along the well tubing. To achieve this, the upper cleaning tool may be adapted to initially be provided in a deactivated configuration permitting fluid flow past the tool, whilst the lower cleaning tool may be adapted to be provided in an activated configuration, restricting fluid flow past the tool so as to urge fluid along the well tubing and past the upper tool during movement of the lower cleaning tool. Once the lower tool has been brought adjacent to the upper tool, the upper tool may be adapted to be moved to an activated configuration, to restrict fluid flow past the upper tool. It will be understood that references herein to upper and lower cleaning tools are relative to the apparatus when assembled and prior to running-in to well tubing, which may be deviated from the vertical.

The apparatus may comprise a flow restrictor such as a ball, dart or the like, the restrictor adapted to be located within the support string, to define a barrier between fluid within the string above the restrictor and fluid below the restrictor. The flow restrictor may be adapted to be pumped or passed down the support string using completion fluid such as brine, and may therefore define a barrier between the completion fluid and fluid present in the well and in the string below the restrictor. This avoids or substantially reduces any interface between fluids such as drilling mud in the well tubing and the completion fluid. The flow restrictor may be adapted to be passed down the support string prior to or during translation of the cleaning tool relative to the well tubing. In this fashion, drilling mud and other fluid removed from the well tubing using the cleaning tool may be replaced with clean completion fluid, preparatory to completion of the well. The apparatus, in particular the cleaning tool, may comprise a catcher or the like for catching or retaining the flow restrictor to prevent discharge of the flow restrictor into the well tubing. The apparatus, in particular the cleaning tool, may also comprise a bypass such as a bypass port adapted to permit fluid flow past the restrictor once the flow restrictor has seated on the catcher. This facilitates flow of completion fluid or the like past the restrictor to replace fluids removed from the well tubing. The apparatus may also comprise a valve seat for the restrictor, or a separate valve or the like, for preventing return flow of fluid up the support string past the restrictor.

Further features of the cleaning tool of the cleaning apparatus are defined above.

According to a third aspect of the present invention, there is provided a method of cleaning a well, the method comprising the steps of:

locating a well cleaning tool in well tubing to be cleaned on an associated support string; configuring the well cleaning tool to prevent fluid flow past the tool; and translating the well cleaning tool relative to the well tubing to displace fluid along the well tubing to thereby clean the well.

The method may comprise translating the cleaning tool along the support string relative to the well tubing from a downhole location and in a direction towards the surface, to displace fluid in the well tubing along the tubing to surface. Replacement fluid such as completion fluid may be pumped into the well tubing down the support string, to create a pressure differential across the tool and urge the cleaning tool along the support string.

Alternatively, the cleaning tool may be translated along the support string relative to the well tubing in a direction from surface to a downhole location, to displace fluid in the well tubing and up the support string to surface. Replacement fluid such as completion fluid may be pumped into the well tubing down the annulus, to create a pressure differential across the tool and urge the cleaning tool along the string.

In a further alternative, the cleaning tool may be secured relative to the support string and translated relative to the well tubing in a direction towards the surface, to displace fluid in the well tubing along the tubing to surface, by translating the support string along the well tubing. Replacement fluid such as completion fluid may be pumped into the well tubing along the support string. In a variation, the cleaning tool may displace fluid along the well tubing during run-in of the support string, with displaced fluid passed to surface through the support string and completion fluid pumped into the well tubing behind the cleaning tool.

The method may comprise cleaning a first section of well tubing of a first diameter using a first cleaning tool of a corresponding first, cleaning diameter, and cleaning a second section of well tubing of a second diameter using a second cleaning tool of a corresponding second, cleaning diameter.

Preferably, a lower cleaning tool is provided and is secured against movement relative to the support string, and an upper cleaning tool is provided and is movably mounted relative to the support string. The support string may be translated within and relative to the upper cleaning tool, to carry the lower cleaning tool to a position adjacent to the upper tool to clean a lower section of well tubing, and to carry fluid out of said lower section and past the upper cleaning tool. The upper cleaning tool may then be translated relative to an upper section of well tubing, to carry the fluid displaced from the lower section, as well as fluids in the upper section, along the well tubing. To achieve this, the upper cleaning tool may initially be provided in a deactivated configuration permitting fluid flow along the annulus past the tool, whilst the lower cleaning tool may be provided in an activated configuration, restricting fluid flow past the tool so as to urge fluid along the well tubing during movement of the lower cleaning tool. Once the lower tool has been brought adjacent to the upper tool, the upper tool may be moved to an activated configuration, to restrict fluid flow past the upper tool.

The method may further comprise defining a barrier between fluid in the well tubing and replacement fluid, such as completion fluid, pumped into the well tubing. The barrier may be defined by a flow restrictor or the like, which may be run into the well tubing through the support string, and which may define a barrier between fluid within the string above the restrictor and fluid below the restrictor. The flow restrictor may be adapted to be passed down the support string prior to or during translation of the cleaning tool relative to the well tubing. The flow restrictor may engage a catcher to prevent discharge of the flow restrictor into the well tubing. Once the flow restrictor has seated on the catcher, bypass flow around the restrictor may be permitted, to facilitate flow of completion fluid or the like past the restrictor to replace fluids removed from the well tubing.

According to a fourth aspect of the present invention, there is provided a well cleaning tool for location in well tubing to be cleaned on an associated support string, the cleaning tool adapted to be configured to restrict fluid flow past the tool along an annulus defined between the well tubing and the support string, such that translation of the cleaning tool relative to the well tubing urges fluid in the well tubing along the annulus to thereby clean the well tubing.

Embodiments of the present invention will now be described by way of example only, with reference to the accompanying drawings, in which:

FIG. 1 is a schematic, longitudinal part-sectional view of apparatus for cleaning a well and of a well cleaning tool forming part of the cleaning apparatus, in accordance with a preferred embodiment of the present invention, the tool and apparatus shown during an initial step in a method of cleaning a well; and

FIGS. 2 to 5 are views of the cleaning tool and apparatus during further steps in the method of cleaning a well.

Turning firstly to FIG. 1, there is shown apparatus for cleaning a well in accordance with a preferred embodiment of the present invention, the apparatus indicated generally by reference numeral 10 and including a well cleaning tool indicated generally by reference numeral 12. The apparatus 10 is shown in FIG. 1 during run-in to a well borehole 16 which has been drilled from surface and lined with well tubing 14. Specifically, the borehole 16 has been drilled to a first depth and a casing 18, comprising a number of threaded casing sections coupled together end-to-end, has been located in the drilled section and cemented in place. An extension 20 has then been drilled and a smaller diameter liner 22, also comprising a number of tubing sections coupled together end-to-end, has been installed in the section 20 extending from the lower end or shoe 24 of the casing 18, and also cemented in place.

As will be understood by persons skilled in the art, the casing 18 and liner 22 initially contain a volume of fluids such as drilling mud and formation fluids, and solids such as drill cuttings, cement residue and the like. These fluids and solids must be removed from the well tubing 14 before the well can be completed by running in a completion string to gain access to well fluids in a particular rock formation. As discussed above, this has conventionally been achieved by pumping pills of viscous fluid down a tubing string (not shown) located in the well tubing 14, followed by a completion fluid such as brine. These viscous pills transport fluids and entrained solids along the well tubing 14 to surface along an annulus defined between the tubing string and the well tubing 14. A filtering tool may then be utilised to filter out remaining solids present in the well tubing 14. However, as discussed above, this prior art procedure suffers from various disadvantages which are obviated by the present invention.

The cleaning apparatus 10 of the present invention is shown in FIGS. 1 to 5 at various stages in a method of cleaning the well tubing 14 utilising the cleaning apparatus 10. For ease of illustration, only part of the borehole 16 is shown, in FIG. 1.

As shown in FIGS. 1 to 5, the cleaning apparatus 10 generally comprises a support string 26 adapted to be located in the well tubing 14 to be cleaned, and at least one well cleaning tool 12 in the form of a plug or swab which is adapted to be configured to restrict fluid flow past the tool. In the illustrated embodiment, the apparatus 10 comprises two such well cleaning tools 12 and 12 a, and the cleaning tools 12, 12 a are adapted to be translated relative to the well tubing 14 to displace fluid along the tubing to thereby clean the well.

In more detail, the cleaning apparatus 10 includes an upper cleaning tool in the form of the tool 12, and a lower cleaning tool in the form of the tool 12 a. The lower cleaning tool 12 a is secured to an end 30 of the support string 26, whilst the upper cleaning tool 12 is mounted for selective movement relative to the string 26. Each of the cleaning tools 12, 12 a are moveable between a first, deactivated configuration where they permit fluid flow and a second, activated configuration where they restrict fluid flow.

The cleaning tools 12, 12 a are both shown in FIG. 1 in deactivated configurations, during run-in to the well tubing 14. In this configuration, the upper cleaning tool 12 is initially retrained against movement relative to the support string 26 by a shear pin or locking ring, or by a shoulder or upset (not shown) on the support string 26.

The upper cleaning tool 12 is of a larger external diameter than the lower cleaning tool 12 a, and serves for cleaning the larger diameter casing 18, whereas the lower cleaning tool 12 a serves for cleaning the smaller diameter liner 22. The cleaning tool 12 comprises a plurality of abutting elements in the form of fins or ridges 32 provided on a body 34 of the tool 12, which define a wiper for cleaning an inner surface of the well tubing 14. It will be understood that like components of the lower cleaning tool 12 a with the upper tool 12 are indicated by the same reference numerals, with the addition of the suffix a.

The cleaning tools 12, 12 a each include an actuating mechanism (not shown) for moving the fins 32 between retracted and extended positions corresponding to the deactivated and activated configurations of the tools. The actuating mechanism may be a hydraulic actuator such as a piston, a mechanical actuator such as a mandrel and cam surface arrangement, or a suitable electro-mechanical actuator. In each case, the actuating mechanism serves for axially compressing the body 34, to urge the fins 32 radially outwardly into abutment with the well tubing wall. The fins 32 thus abut or engage the inner wall of the casing 18/liner 22 to restrict fluid flow past the tool 12, 12 a. In this fashion, subsequent translation of the tool 12, 12 a relative to the casing 18/liner 22 displaces fluid along the well tubing, to clean the well.

The cleaning apparatus 10 is shown in FIG. 2 following location of the upper cleaning tool 12 at a junction 36 between the casing 18 and liner 22, with the lower cleaning tool 12 a located partway along a length of the liner 22. The upper cleaning tool 12 is then released to permit movement of the support string 26 relative to the upper tool, such that the lower cleaning tool 12 a may be advanced along the liner 22 and located adjacent an end or shoe 38 of the liner 22, as shown in FIG. 3. It will be noted that the string 26 may carry further tools such as a jetting sub 39, bypass sub 41 and a scraper 43, if required for a particular downhole operation.

A flow restrictor in the form of a ball 40 is then inserted into the support string 26 at surface and is pumped down the string to the lower cleaning tool 12 a. The ball 40 forms a barrier between drilling mud 42 in the string 26 below the ball 40 and in the casing 18/liner 22, and completion brine 44 behind the ball 40, which is used to pump the ball 40 down the string. In this regard, where the weight of the brine 44 pumped into the tubing 14 is similar to or less than that of the mud 42, it may be desired or necessary to maintain the brine pressure higher than that of the mud to avoid mud leakage across the tool 12.

When the ball 40 reaches the end of the string 26, it is caught by a ball catcher 44 in the lower tool 12 a, shown in FIG. 4, which prevents discharge of the ball 40 into the liner 22. The lower cleaning tool 12 a also includes a bypass port for fluid bypass around the ball 40 once the ball has seated on the ball catcher 44, to enable the completion brine to be pumped into the liner 22, to replace displaced drilling mud. Accordingly, as the ball 40 passes down the string 26, drilling mud 42 in the string 26 is pumped out of the string though the bypass port, and flows up around the cleaning tool 12 a into the annulus 28 and thus to surface. The support string 26 is then filled with clean completion brine 44 and a small volume of drilling fluid 42 (if any) remains in the liner 22 below the lower cleaning tool 12 a.

After the ball 40 has been collected by the ball catcher 44, the lower cleaning tool 12 a is moved to the activated configuration by the actuating mechanism, which urges the fins 32 a radially outwardly into abutment with an inner wall 46 of the liner 22. In this position, the fins 32 a restrict fluid flow past the lower cleaning tool 12 a, facilitating displacement of fluid along the liner 22. The support string 26 is then retracted through the upper cleaning tool 12 whilst completion brine is pumped into the liner 22 through the string 26. The lower cleaning tool 12 a thus defines a barrier between the drilling mud in the liner above the tool 12 a and the completion brine pumped into the liner 22 below the tool 12 a.

As the lower tool 12 a is translated towards the upper tool 12, the fins 32 a scrape or wipe clean the inner wall 46 of the liner 22, removing any adhered solids such as mud residue. The tool 12 a thus drives the scraped solids and the drilling mud along the liner 22, and past the upper cleaning tool 12 through annulus 28 and along an annulus (not shown) between the tool 12 and string 26, and thus to surface, as shown in FIG. 4.

This movement of the lower cleaning tool 12 a is continued until the lower tool is brought to a position where the upper tool 12 is seated on the lower tool 12 a, with the lower tool remaining in the liner 22. The upper cleaning tool 12 is then moved to the activated configuration by urging the fins 32 radially outwardly into engagement with the casing wall 48, as shown in FIG. 5. The tool 12 is also sealed relative to the string 26.

The upper cleaning tool 12 thus forms a barrier between the drilling mud 42 in the annulus 28 above the tool 12 and the clean completion brine 44 pumped into the liner 22 and casing 18 below the upper tool 12. The support string 26 is then translated further along the casing 18, carrying the upper tool 12, whilst pumping further brine 42 through the string 26 and into the well tubing 14. In a similar fashion to the lower cleaning tool 12 a, the fins 32 of the upper tool 12 scrape clean the inner wall 48 of the casing 18, to remove any adhered solids. The cleaning apparatus 10 is then returned to surface, carrying the drilling mud and entrained solids, and the drilling mud may be cleaned for subsequent re-use. The well tubing 14 has thus been cleaned and the fluid present in the tubing 14 removed to surface and replaced with clean completion brine.

The apparatus and method of the present invention offers significant advantages over prior cleaning methods and apparatus. For example, the apparatus and method of the invention avoids creating a large fluid interface, by providing a barrier between the fluids. Also, mechanical interference between the cleaning tools 12, 12 a and the well tubing 14 wipe the tubing to provide superior, assured cleaning of mud and solids from the well. There is no need to store chemicals for use in viscous pills, with associated Health & Safety benefits, and there is a reduced requirement to use and clean mud pits, this also freeing up deck space for other equipment. In use, it is not necessary to circulate at high fluid flow rates whilst rotating the support string, with associated time and cost savings. The weight of the apparatus is also much reduced compared with prior cleaning assemblies.

Various modifications may be made to the forgoing within the scope of the present invention.

For example, in an alternative embodiment, the apparatus 10 may be run-in to the well tubing 14 with the cleaning tools 12, 12 a in their respective activated configurations, so that the tools wipe the casing 18 and liner 22 during their passage down through the tubing. In this case, drilling mud and scraped solids may be driven ahead of the tools 12, 12 a and removed from the well tubing 14 along the string 26 to surface, with completion brine pumped into the well tubing behind the cleaning tools 12, 12 a. The string may include suitable valves or the like to ensure the mud does not return into the well through the string 26. Once the apparatus 10 has been fully run-in, the cleaning tools 12, 12 a may then be moved to their deactivated configurations for removal of the apparatus from the tubing 14, with additional brine pumped downhole during run-out.

In a further alternative embodiment, the or each of the tools 12, 12 a may be movably mounted on the support string 26, which may be already located within the well tubing 14. The tools 12, 12 a may be pumped downhole from surface by the completion fluid, by creating a positive pressure differential across the tool, the tools 12, 12 a wiping the casing 18/liner 22 wall during passage downhole, and driving drilling mud and the like into the string 26 and thus to surface. The tools 12, 12 a may then be discharged into a rathole (not shown) at the bottom of the borehole 16.

In a still further alternative embodiment, the or each of the tools 12, 12 a may again be movably mounted on the support string 26, and the apparatus 10 may be located downhole with the tools 12, 12 a in their deactivated configurations. The tools may then be moved to the activated configuration and pumped to surface along the string 26 by completion fluid passed down the string 26, to create a positive pressure differential across the tool. The tools 12, 12 a may thus wipe the casing 18/liner 22 wall during passage to surface, driving drilling mud and the like along the well tubing 14.

In a yet further alternative embodiment, the tools 12 and/or 12 a may be configured to permit fluid flow in one direction and to restrict fluid flow in a second, opposite direction past the tool. For example, The cleaning tools 12, 12 a may be adapted to be configured such that when the tool is translated in a first direction along a length of the well tubing 14, fluid flow past tool is permitted; and when the tool 12, 12 a is translated in a second, opposite direction along the length of the tubing 14, fluid flow past the tool is restricted. Thus fluid flow past the tools 12, 12 a may be permitted during run-in of the tool into the well tubing 14, and restricted when the tool is pulled-out of the well tubing. The first direction may therefore be a run-in direction and the second direction a pull-out or run-out direction. Alternatively, fluid flow past the tools 12, 12 a may be restricted during run-in, and permitted when the tool is pulled-out of the well tubing 14. The first direction may therefore be a run-out direction and the second direction a run-in direction. To achieve this, the cleaning tool may include an abutting element in the form of a resilient, annular ring or the like, which may scrape the well tubing when passed in one direction and be deflected when passed in the opposite direction.

The cleaning tool may be adapted to be run on wireline or slickline. 

1. A well cleaning tool for location in well tubing to be cleaned on an associated support string, the cleaning tool adapted to be configured to restrict fluid flow past the tool and to be translated relative to the well tubing to displace fluid along the well tubing and thereby clean the well.
 2. A well cleaning tool as claimed in claim 1, wherein the tool is adapted to be configured such that fluid flow past the tool is substantially prevented.
 3. A well cleaning tool as claimed in claim 1, wherein the tool is adapted to be configured to restrict fluid flow past the tool along an annulus defined between the well tubing and the support string.
 4. A well cleaning tool as claimed in claim 1, wherein the cleaning tool is movable between a first configuration where fluid flow past the cleaning tool is permitted, and a second configuration where fluid flow past the cleaning tool is substantially prevented.
 5. A well cleaning tool as claimed in claim 4 wherein the first configuration is a deactivated, running configuration, and the second configuration is an activated, cleaning configuration.
 6. A well cleaning tool as claimed in claim 1, wherein the cleaning tool is adapted to permit fluid flow in one direction past the tool, and to restrict fluid flow past the tool in an opposite direction.
 7. A well cleaning tool as claimed in claim 1, wherein the cleaning tool is arranged such that the tool automatically restricts fluid flow when the tool is translated in one direction along the well tubing, but permits fluid flow when the tool is translated in an opposite direction.
 8. A well cleaning tool as claimed in claim 1, wherein the cleaning tool is adapted to abut a wall of the well tubing in order to restrict fluid flow.
 9. A well cleaning tool as claimed in claim 1, wherein the cleaning tool is coupled to tubing of the support string.
 10. A well cleaning tool as claimed in claim 9, wherein the tubing of the support string is adapted to permit flow of completion fluid therethrough and into the well.
 11. A well cleaning tool as claimed in claim 1, wherein the cleaning tool comprises at least one abutting element for abutting the wall of the well tubing, the element serving for permitting and restricting fluid flow past the tool.
 12. A well cleaning tool as claimed in claim 11, wherein the abutting element is movable between a deactivated configuration and an activated configuration, which corresponds to deactivated and activated configurations of the tool, for selectively engaging an internal surface of the tubing.
 13. A well cleaning tool as claimed in claim 10, wherein the abutting element is adapted to be biased into abutment with the well tubing wall.
 14. A well cleaning tool as claimed in claim 4, wherein the tool comprises an actuating mechanism for moving the tool between the deactivated and activated configurations.
 15. A well cleaning tool as claimed in claim 14, wherein the actuating mechanism is adapted to exert a radial actuating force on the abutting element.
 16. A well cleaning tool as claimed in claim 10, wherein the abutting element defines a cleaning surface for cleaning an internal wall of the well tubing during translation of the cleaning tool through the tubing.
 17. A well cleaning tool as claimed in claim 16, wherein the cleaning tool is adapted to be movably mounted relative to the support string, and comprises a body mounted for movement relative to the support string along a length thereof.
 18. Apparatus for cleaning a well, the apparatus comprising: a support string adapted to be located in well tubing to be cleaned; at least one well cleaning tool coupled to the support string, the well cleaning tool adapted to be configured to restrict fluid flow past the tool and to be translated relative to the well tubing to displace fluid along the well tubing and thereby clean the well.
 19. Apparatus as claimed in claim 18, wherein the apparatus comprises a plurality of cleaning tools, and comprises a first cleaning tool adapted to define a first cleaning diameter for cleaning a first section of well tubing of a corresponding first diameter and a second cleaning tool adapted to define a second cleaning diameter for cleaning a second section of well tubing of a corresponding second diameter.
 20. Apparatus as claimed in claim 19, wherein at least one of the cleaning tools is adapted to be movably mounted relative to the support string, and comprises a body mounted for movement relative to the support string along a length thereof.
 21. Apparatus as claimed in claim 19, wherein at least one of the cleaning tools is movable relative to at least one other cleaning tool.
 22. Apparatus as claimed in claim 19, wherein a lower cleaning tool is secured against movement relative to the support string, and an upper cleaning tool is movably mounted relative to the support string.
 23. Apparatus as claimed in claim 19, wherein upper cleaning tool is adapted to initially be provided in a deactivated configuration permitting fluid flow past the tool, lower cleaning tool is adapted to be provided in an activated configuration, restricting fluid flow past the tool so as to urge fluid along the well tubing and past the upper tool during movement of the lower cleaning tool.
 24. Apparatus as claimed in claim 18, wherein the support string is adapted to permit fluid to be pumped therethrough and into the well to facilitate cleaning the wellbore.
 25. Apparatus as claimed in claim 18, wherein the apparatus comprises a flow restrictor, the restrictor adapted to be located within the support string, to define a barrier between fluid within the string above the restrictor and fluid below the restrictor.
 26. Apparatus as claimed in claim 25, wherein the flow restrictor is adapted to be pumped down the support string using completion fluid for defining a barrier between the completion fluid and fluid present in the well and in the string below the restrictor.
 27. A method of cleaning a well, the method comprising the steps of: locating a well cleaning tool in well tubing to be cleaned on an associated support string; configuring the well cleaning tool to prevent fluid flow past the tool; and translating the well cleaning tool relative to the well tubing to displace fluid along the well tubing to thereby clean the well.
 28. A method as claimed in claim 27, wherein the cleaning tool is translated along the support string relative to the well tubing in a direction from surface to a downhole location, to displace fluid in the well tubing and up the support string to surface.
 29. A method as claimed in claim 27, wherein the cleaning tool is secured relative to the support string and translated relative to the well tubing in a direction towards the surface, to displace fluid in the well tubing along the tubing to surface, by translating the support string along the well tubing.
 30. A method as claimed in claim 27, wherein the method comprises the step of defining a barrier between fluid in the well tubing and replacement fluid pumped into the well tubing. 